The invention relates to a multi-layer film structure having a metallized surface.
The bonding of metals, such as, aluminum, silver, chromium, etc., to plastic films has allowed such films to replace metallic foils in many instances. The flexibility of the films necessitates the formation of a strong metal-plastic bond, and a number of approaches have been developed for providing such bonding.
In U.S. Pat. No. 4,345,005, the disclosure of which is incorporated herein by reference in its entirety, a homopolymer polypropylene core layer is coextruded with an ethylene propylene copolymer. The film is biaxially oriented and the copolymer layer is corona discharge treated. Thereafter, a metal coating is deposited onto the corona discharge treated layer by any suitable process such as, vacuum deposition. In order to enhance adhesion between the metal and plastic film, neither the core layer or outer layer(s) contain a slip agent in an amount which would deleteriously affect the metal/polymer bond. The resulting product has utility in flexible packaging. Polypropylene film employed for packaging purposes inherently permits the transmission of oxygen and water vapor from the outside of the film to the inside of package made up of the film. Oxygen and water vapor promote rapid deterioration of foods packaged in such a container, therefore, its exclusion or control is desired.
U.S. Pat. No. 5,192,620 to Chu et al, incorporated herein by reference discloses a metallized film combination having an oriented polypropylene substrate layer having on one surface a coating of a blend of (a) a vinyl alcohol homopolymer or copolymer, and (b) an ethylene-acrylic acid copolymer as metal-adhesion promoting agent, the coating blend having a metal layer thereon. However, it would be advantageous to provide a coating of vinyl alcohol homopolymer or copolymer without additional components because of the desired oxygen barrier properties of vinyl alcohol polymers.
U.S. patent application Ser. No. 08/258,316, filed Jun. 10, 1994 discloses a metallized multilayer film comprising a polypropylene substrate modified by a maleic anhydride modified propylene polymer, which can be located on a surface of the substrate having a skin layer of polyvinyl alcohol which is capable of being metallized.
It is an object of the present invention to present a metallized film and a method of forming the same which has a decreased oxygen transmission and water vapor transmission rate.